THE MITOCHONDRIAL HISTONE HM - AN EVOLUTIONARY LINK BETWEEN BACTERIALHU AND NUCLEAR HMG1 PROTEINS

The mitochondrial histone HM is a very abundant protein in yeast mitoc hondria that wraps DNA and activates transcription in vitro and is req uired within the cell for proper maintenance of the mitochondrial chro mosome. HM and the bacterial histone like protein HU have similar acti vities in vitro and can substitute for each other in E coli cells and in yeast mitochondria. HM also appears to be functionally homologous t o nuclear HMG1 proteins, with which it shares a high degree of sequenc e homology. We report here the isolation of extragenic suppressors of the yeast HM mutant temperature-sensitive phenotype. We also examined the effects of the lack of HM protein and of respiration deficiency on yeast cells mutant for the NHP6 proteins, the putative yeast nuclear HMG1 homologues.